Mineralogical study of the La Hueca Cretaceous Iron-Manganese deposit, Michoacán, south-western Mexico

Abstract

In this work we describe for the first time the mineralogy and very briefly the possible origin of a banded Fe-Mn deposit associated with a Cretaceous volcanosedimentary sequence of the southern Guerrero terrane, near the sulfide massive volcanogenic deposit of La Minita. The deposit is confined within a felsic tuff unit; about 10 meters thick where sampled for chemical analysis. Using XRF, EDS and XRD techniques, we found besides todorokite, cryptomelane, quartz, romanechite (psilomelane), birnessite, illite-muscovite, cristobalite, chlorite, barite, halloysite, woodruffite, nacrite or kaolinite, and possibly hollandite-ferrian, as well as an amorphous material and two unknown manganese phases.

Although the manganese and iron minerals that characterize the La Hueca site were apparently somewhat altered by diagenetic or weathering processes, the combined evidence of finely banded to laminated structure, the abundant presence of Fe, Mn, Ba, Zn, and Si, and a mineralogy of probable primary originm here represented by hematite, jasper and manganese minerals enriched in zinc and barium, strongly support the interpretation that La Hueca is essentially of sedimentary origin, precipitated from hydrothermally metal-enriched solutions. The deposit is here interpreted as a distal exhalite derived from the same hydrothermal solutions that formed the barite-sulfides deposits of La Minita.